We report on the facile solid-state synthesis and characterization of Li7SiPS8, a new member of the tetragonal LGPS (Li10GeP2S12)-type of ultrafast Li⁺ solid electrolytes. We analyze the structure, phase stability, as well as Li⁺ conductivity of tetragonal and orthorhombic LSiPS by pulsed field gradient NMR and impedance spectroscopy, which show conductivities at RT of up to 2 mScm^-1. While ranking tetragonal LiSiPS as an ultrafast solid electrolyte, the observed conductivity is unexpectedly low compared to other members of this solid solution system. Utilizing solid-state NMR, quantitative phase analysis, and impedance spectroscopy we identify an amorphous thiophosphate side phase with low Si content, which limits the intergrain conductivity and, hence, a potentially higher total conductivity. This case study thus highlights the need for comprehensive structure analysis of LGPS-type materials beyond the crystalline fractions to fully characterize the structure - property relationships in these glass ceramic compounds.

The crystal structure of the title compound, hexaaquadichloridoeuropium(III) chloride, was redetermined with modern crystallographic methods. In comparison with the previous study [Lepertet al.(1983).Aust. J. Chem.36, 477–482], it could be shown that the atomic coordinates of some O atoms had been confused and now were corrected. Moreover, it was possible to freely refine the positions of the H atoms and thus to improve the accurracy of the crystal structure. [EuCl₂(H₂O)₆]Cl crystallizes with the GdCl₃·6H₂O structure-type, exhibiting discrete [EuCl₂(H₂O)₆]⁺cations as the main building blocks. The main blocks are linked with isolated chloride anionsviaO—H...Cl hydrogen bonds into a three-dimensional framework. The Eu³⁺cation is located on a twofold rotation axis and is coordinated in the form of a Cl₂O₆square antiprism. One chloride anion coordinates directly to Eu³⁺, whereas the other chloride anion, situated on a twofold rotation axis, is hydrogen bonded to six octahedrally arranged water molecules.

The title compounds were synthesized via reaction of quartz and AO₂ (A = Rb, Cs) with the elemental alkali metals. Their crystal structures were determined on the basis of single crystal X-ray data. All compounds crystallize in the monoclinic system with space group P2₁/c and lattice constants a = 656.0(l)/684.7(3), b = 1329.7(3)/1375.7(4), c = 1647.6(3)/1703.6(8) pm, β = 107.78(3)/108.23(2)°, Z = 4 (A₆[Si₃O₉], A = Rb/Cs) and a = 668.59(8)/711.4(1), b = 911.37(9)/952.1(2), c = 1121.09(9)/1192.7(7) pm, β = 125.52(9)/126.22(3)°, Z = 2(A₆[Si₂O₇], A = Rb/Cs) respectively. The rubidium and cesium compounds are isotypic with the corresponding potassium silicates.